This application is based on Patent Application No. 2000-385460 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lens driving apparatus, and specifically relates to a lens driving apparatus for driving a plurality of lens groups.
2. Description of the Related Art
A lens driving apparatus 18 for independently driving individual lens holders 5 and 6 via actuators 10a and 10b of a friction drive type which exert a drive force via friction bonding as shown in FIG. 1 has been proposed as a zoom lens for a compact photographic device.
The actuators 10a and 10b have bases 1a and 1b and drive shafts 3a and 3b respectively attached to an end of piezoelectric elements 2a and 2b in the extension-contraction direction. The drive shafts 3a and 3b are friction bonded to lens holders 5 and 6 via a force exerted by flat springs 4a and 4b (only 4b is shown in the drawing) set in a channel in the lens holders 5 and 6. When a drive voltage having, for example, a sawtooth pulse waveform is applied to the piezoelectric elements 2a and 2b, the drive shafts 3a and 3b are oscillated at different speeds in the axial direction as indicated by the arrows 90 and 92, such that the lens holders 5 and 6 are moved along the drive shafts 3a and 3b. The lens holders 5 and 6 are guided in the optical axis direction by a guide shaft 8, and the photographic element 7 is disposed on the focal plane of the optical system.
In the lens driving apparatus 18, since the lens holders 5 and 6 are independently and individually moved to optional positions by the respective actuators 10a and 10b, each lens holder 5 and 6 must have a specific positional relationship to obtain a desired photographic magnification and photographic distance. Particularly when zooming, the positions of the lens holders 5 and 6 must be detected with high precision in order to control the position of the lens holders 5 and 6.
Magnetic plates 11a and 11b are mounted on the respective lens holders 5 and 6, and MR sensors 12a and 12b (only sensor 12b is shown in the drawing) are provided on the frame opposite these magnetic plates 11a and 11b, such that the position of the lens holders 5 and 6 can be measured. Furthermore, a signal processing device is also required to control the drive of the respective actuators 10a and 10b based on the measurement data. It is difficult to make the lens driving device compact and of simple structure due to the use of the sensors and signal processing device.
Accordingly, the technical problem resolved by the present invention is to provide a compact lens driving apparatus for driving a plurality of lenses, or a lens driving apparatus of simple structure.
The present invention focuses on the fact that normally each lens holder need not necessarily be moved since the relationship between the photographic magnification and the lens holder position is completely determined, and provides a lens driving apparatus having the following structure.
The lens driving apparatus is a type which drives in the optical axis direction a first and a second lens group arranged in the optical axis direction. The lens driving apparatus comprises first and second cam followers extending mutually parallel in a right angle direction to the optical axis from the first and second lens groups, cam member having first and second cams arranged along the optical axis and respectively engaging the first and second cam followers, first drive means for driving the first lens group in the optical axis direction, and second drive means for driving the second lens group in the optical axis direction.
In this structure, the cam member is not limited to a plate cam, and also may be, for example, a cylindrical cam member (cam drum).
According to this structure, for example, the second drive means exerts a supplemental force in the direction of movement of the second lens group, such that the second cam follower moves along the second cam of the cam member in conjunction with the drive of the first drive means, and the movement of the second cam follower is supplemented relative to the second cam of the cam member.
In this way, a smooth drive is possible and the cam member and first drive means can be compact even when it is difficult for the second lens group to move because the pressure angle of the second cam is large, and a large drive force is required for only the first drive means.
If the endface of the cam member is used as a cam (e.g., a plate cam), the cam member can be made even more compact by suitably controlling the first and second drive means so as to have the first and second cam follower follow the endface of the cam member.
Accordingly, it is unnecessary to detect the position of each lens group or control the drive of each lens group, and the lens driving apparatus can be made more compact.
It is desirable that the second cam of the cam member has first and second cam surfaces which are mutually opposed and have a gap therebetween wider than the second cam follower. The control means is linked to the drive of the first drive means, and the first and second drive means are controlled such that the second cam follower moves in the optical axis direction selectively along the one or another of the first or second cam surface of the second cam of the cam member.
In this structure, the position of the second lens group relative to the first lens group is different when the second cam follower is along the first cam surface of the second cam of the cam member, and when the second cam follower is along the second cam surface of the second cam of the cam member.
In this way, the lens groups can be moved in different modes, for example, for normal photography and macro photography.
The technical idea of switching the cam surface abutting the cam follower is widely suited to lens driving apparatuses, and the present invention provides a lens driving apparatus having the following structure.
The lens driving apparatus is a type which moves in the optical axis direction a first and a second lens group arranged in the optical axis direction. The lens driving apparatus comprises first and second cam followers, cam member, drive means, and force exerting means. The first and second cam followers extend in a right angle direction to the optical axis from the first and second lens groups. The cam member has first and second cams which respectively slide on the first and second cam followers. The second cam has first and second cam surfaces which are mutually opposed and have a gap therebetween wider than the second cam follower. The drive means drives the first lens group. The force exerting means selectively exerts a force on the second lens group in bilateral directions along the optical path such that the second cam follower selectively abuts the first or second cam surface of the second cam of the cam member.
In this structure, the cam member is not limited to a plate cam, and also may be, for example, a cylindrical cam used in replaceable lenses of single lens reflex cameras. The force exerting means may be an actuator capable of driving the second lens group in bilateral directions along the optical path, and may switch the direct of the exerted force by, for example, a spring.
According to this structure, the force exerting means switches the cam surface abutting the second cam follower by switching the direction of the force exerted on the second lens group, so as to drive the lens by selecting one of two modes of different positions of the second lens group relative to the first lens group.
In the lens driving apparatus having the aforesaid structures, it is desirable that the drive means is a drive means of the friction drive type including a drive force generator for generating a drive force for driving the lens group, and a drive force transmitter for transmitting a drive force from the drive force generator to the lens group via a friction force.
When a drive means of the friction drive type is used, the apparatus is easily made more compact. Furthermore, when a drive means is used for switching the cam surface abutting the cam follower, the control of the drive means is simple since any imbalance of the load is absorbed by sliding on the friction surface.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.